The present invention relates to automatic feedback control of the planarity of rolled stock, and more particularly the invention relates to such a control device which includes measuring equipment for measuring planarity and adjusting structure for eliminating defects and errors in planarity under utilization of desired values being inputed either manually or can be called up automatically.
During the rolling of flat stock and only after the onset of rolling and only after a thread-in phase will the rolling speed be increased to the normal operating speed. In most materials such a change in speed is equivalent to a change in deforming speed will experience a change in internal strength and resistance which has to be considered. Generally speaking any change in rolling speed goes hand-in-hand with a change in rolling force. This change in rolling force in turn changes the thickness of the flat stock. Therefore, it is necessary to control in some fashion the rolling process by keeping the thickness of the roll stock constant through the control of the rolling force. The rolling force being therefore an adjustment parameter by means of which the thickness of the rolled stock can be varied. However, the problem is more complex. The desired qualities are not obtainable simply through modifying the rolling force unless a companion deformation, being an elastic one, of the working or the support rolls in the mill stand are taken into consideration. Therefore, whenever change occurs in the profile of the strip or rolled stock cross section one has to expect some interference with overall planarity.
Generally speaking it is known to provide a closed loop feedback type of control to eliminate the effect changes in the rolling force have on the planarity of the rolled stock. This procedure requires ascertaining any errors or deviation of planarity by an appropriate measuring system. The measurement of planarity may be carried out by instruments of a contact variety or of the noncontact variety; the measuring method may operate indirectly by ascertaining planarity for example through measuring the internal tension in the strip or by providing some indication of any waviness in the surface of the rolled stock.
Whatever mode of measurement one employs there is the inherent defect or detriment that the planarity based on the type of measurement used can be ascertained only at a certain distance from the rolling gap. In other words the error in planarity has well occurred and may already persist to some extent before it can be recognized in the flat stock as emerging from the rolling mill. The known system, moreover, is capable of determining errors in planarity as they are produced in the rolling gap only on a compounded integrated basis so that any feedback control principles taking this integration into consideration are not sensitive and are in fact unsuitable to offset e.g. temporary errors in planarity as they may occur for example on the basis of temporary speed variations or strip tension variations as they produce temporary changes in the rolling force. For this reason it is customary for instance to turn the feedback control loop off during the beginning stages of rolling and during threading of the rolled stock throught the mill. Instead, the (human) operator will manipulate the process during these stages based on his experience and visual impression and with whatever success he can master.